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Distillation and Alcohol

Introduction

We have discussed what is involved in the fermentation of sugar to alcohol and by
this time many of you have direct experience of this process. The fermentation of
alcoholic beverages is a technology that dates back to the stone age. The
separation of the alcohol from the water, on the other hand, is a
relatively recent development. The Chinese were distilling rice beer as
early as 800 BC. But the separation of ethyl alcohol as a substance was not
achieved in Europe until the 12th century AD. At that time it was regarded
by the alchemists as a "fifth essense" or "quintessence," a higher form of water
which was capable of dissolving many medicines which were not soluble in ordinary water.
The use of alcohol for medicinal purposes is reflected in another common name for
alcohol: aqua vitae (water of life), a name which survives as the name of a modern
liqueur.

The principle problem of the preparation of alcohol is that yeasts are unable
to ferment a liquid which is more than about 18% alcohol. It is useful to view
alcohol as a waste product from the yeast's point of view. Beyond about 18%
they simply cannot live in their own "urine." We start, then, with a liquid
which is between 5% and 15% alcohol and our primary task is to separate the
alcohol from the water and other materials. There are two common methods for doing
this: freezing and boiling.

Recrystalization

We have already discussed the melting and freezing of solutions when we discussed
the difference between quartz and glass. Recall that a pure substance melts and
freezes at a single temperature, that is, the melting point equals
the freezing point. By contrast, a solution melts over a range
of temperatures rather than at a single point. Let us recall the behavior of water
as it freezes.

Pure water freezes at 0 C. Pure ice melts at 0 C. If I start with water at room
temperature and cool it, the temperature will drop. From 25 C (room temperature)
to 20 C, 10 C, 5 C, 0 C. But at 0 C something peculiar happens, ice crystals form.
By the time that half the water has turned to ice, the temperature is still 0 C.
Only after all the water is frozen will the temperature fall to -1 C, -5 C, ...
Similarly if I start with ice at -10 C and warm it, it will warm to -5 C, -1 C,
0 C but then the ice starts to melt. The temperature will stay at 0 C until the
last bit of ice is melted and then will start to rise again.

Solutions behave differently. Let us take mead, for example. As we cool mead
from room temperature, the temperature will fall below 0 C before
the first ice crystals form. And since water freezes at a higher temperature
than alcohol, the first ice to form will be almost pure water ice. That means the
liquid that remains will have a higher percentage of alcohol than the original
liquid. Furthermore, this more concentrated solution will freeze at a lower temperature.
So unlike the case of pure water (or pure alcohol for that matter), the temperature
will continue to drop as the solution freezes. As the water ice freezes out,
the temperature gets lower and lower and the liquid gets more and more concentrated
in alcohol. Finally, the temperature will get so low that the remaining solution
freezes. But if we stop prior to that point, we will have a liquid that is
much higher in alcohol than the original liquid.

There are two ways to look at this. On the one hand, we could consider that we are
purifying the alcohol by removing the water "impurity." On the other hand,
we could consider that we are purifying the water by removing the alcohol
"impurity." Which one is the impurity depends on which one you are most interested
in. In the final analysis it is better to consider this a separation
process rather than a purification process. The separation process
that relies on freezing out one component is called recrystalization.

Distillation

Lets look now at the phenomenon of boiling. Recall that pure water boils at
100 C and water vapor condenses at 100 C. If we heat water from room temperature,
the temperature climbs from 25 C to 50 C to 75 C to 100 C. At 100 C the temperature
stops climbing and the water begins to boil, producing water vapor at 100 C.
As we continue to heat, the temperature stays pegged at 100 C until the last drop
of water has boiled away and only then does the temperature begin to climb again.

By contrast, if we heat a solution like mead, the temperature will climb to the
boiling point of the substance which boils at the lowest temperature. Since
alcohol boils at 78 C and water boils at 100 C, the temperature of the mead
will climb to 78 C and begin to boil. Most of the vapor will be alcohol at this
temperature since water does not boil until 100 C. This leaves less alcohol
and more water in the
mead so the temperature continues to climb as the solution boils.

Now suppose we start with mead that is 5% alcohol. At 78 C most of the vapor will
be alcohol but there will be some water as well. Say this vapor is 60% alcohol.
If we were to condense this vapor into a liquid and then bring it to a boil again,
the new liquid would be 60% alcohol, but the new vapor would be even higher in
alcohol because there was less water to begin with. So the new vapor is, say,
80% alcohol. We can repeat this process over and over again and the alcohol
content will increase with each new vaporization step.

Actually it is not really necessary to break it up into steps. If we pass the vapor
through a tube, some of it will condense on the walls of the tube. As more hot vapor
rises, some of the condenses vapor will re-evaporate and move farther up
the tube. This process is repeated over and over again. As the line of condensation,
or reflux line moves up the tube, or column, the refluxing
liquid gets more and more alcoholic. The liquid in the original flask or
pot gets less and less alcoholic. So again we are really performing
a separation rather than a purification. This kind of separation is
called distillation.

So which is better, recrystalization or distillation? Well, it depends on what you
want. Both will separate two components of a solution, in our case alcohol from
water. In the case of ethanol and water, higher ethanol concentrations can
be achieved from distillation than from recrystalization. For our project, then,
we will choose to distill our mead to get a product that is as high in alcohol
as possible. The test we will apply will be whether the product will burn
(about 50% or 100 proof).

Distillation and the Law

It is illegal to distill alcohol without a permit from the
Bureau of Alcohol, Tobacco, and Firearms (BATF). Recall that adults 21 years of
age and older are allowed to brew up to 100 gallons of wine or beer for their own
consumption. Thus there are homebrewing magazines, clubs, classes, and suppliers
in great numbers. There is no legal equivalent for distilled alcoholic beverages.
You are not allowed to make your own whiskey or vodka, even for your own personal\
use.

There is a provision in the law for the experimental distillation of alcohol as a
fuel. This is not a loophole. It requires a permit from the BATF
and they are serious about the fuel part. The permit is not hard to get but
its provisions are strictly enforced. I applied for and received a permit from the
BATF for the distillation of alcohol fuel in this class. It allows for
the distillation of ethyl alcohol in stills owned by the Chemistry Department
and the alcohol must be used as fuel on the premises. It is under this permit
that you may attempt this project.

It may interest you to know that the Chemistry Department purchases 190 proof
(95%) ethyl alcohol in 55 gallon drums for $3.72 per gallon. This alcohol cannot
be used for beverage purposes. If it were, it would be subject to a Federal
tax of $12.83 per gallon, i.e. the tax is more than three times the purchase price.

Ethanol

When we speak of alcohol in everday language, we are usually talking about
ethanol, or ethyl alcohol. We already know the formula for this compound,
C2H5OH, but we will find that in organic chemistry,
there may be several different compounds with the same name. Increasingly,
we will need to provide more information on the structure of a compound in order
to discuss its properties. Here are several representations of the ethanol molecule:

Charge Distribution

Ball and Stick

Structural Formula

H H
| |
H-C-C-OH
| |
H H

Formula

CH3CH2OH

Emprirical Formula

C2H6O

As we go from left to right, we get less and less information about the molecule,
but the formulas become easier to draw or type. A chemist learns to see that
all five of these representations denote the same molecule. We will use
any of these formats depending on the circumstances.

As you well know, ethanol is soluble in water (e.g. beer, wine, mixed drinks).
But looking at the structures above and recalling the principles learned in the
soap project, we can undestand why this is so. The OH
group in ethanol looks like half a water molecule. In the charge distribution,
this shows up as a deep blue (positive) charge right next to a deep red (negative)
charge. The polarity of the OH group causes a strong attractive force with other
OH groups and so alcohols tend to be soluble in water.

Other Alcohols

You may not realize it, but there is a whole class of organic compounds called
alcohols. You are probably familiar with some of them:

Name

Formula

Household Use

Methanol

H
|
H-C-OH
|
H

gasoline antifreeze, Sterno, "wood alcohol"

Ethanol

H H
| |
H-C-C-OH
| |
H H

"grain alcohol"

Isopropanol

H H H
| | |
H-C-C-C-H
| | |
H O H
H

"rubbing alcohol"

What makes these compounds alcohols is the OH group.
What distinguishes different alcohols from each other is the number of carbon atoms.
The name of the alcohol tells you the number of carbons:

Prefix

Number of Carbons

Methyl

1

Ethyl

2

Propyl

3

Butyl

4

Pentyl

5

Hexyl

6

Heptyl

7

Octyl

8

Nonyl

9

Decyl

10

Some alcohols have
more than one OH group:

Name

Formula

Household Use

Ethylene Glycol

H H
| |
H-C-C-H
| |
O O
H H

automobile antifreeze

Gycerol

H H H
| | |
H-C-C-C-H
| | |
O O O
H H H

component of soap, drugstore "glycerine"

A Model Industry

Once we can make and purify ethanol, we can make a variety of organic compounds
from it. We will use this as a model for an industrial complex. Each of these
substances can be purified by distillation.

Organic Acids

Recall that when mead "goes sour," bacteria digest the ethanol in the presence of
oxygen. The reaction is a typical oxidation:
CH3CH2OH + O2 -----> CH3COOH + H2O
The product is acetic acid (old name) or ethanoic acid, the acid present in vinegar.
Vinegar is typically 5% acetic acid. We can purify it by distillation to produce
concentrated acetic acid, called glacial acetic acid. Like alcohols,
acetic acid contains an OH group and so it is, of course, soluble in water.

Charge Distribution

Ball and Stick

Structural Formula

HO H
| |
O=C-C-H
|
H

Formula

CH3COOH

Emprirical Formula

CH2O

The other alcohols can also be oxidized to their corresponding acids (though
not typically by bacteria).

Ethylene and Ethyl Ether

Recall that concentrated sulfuric acid can literally suck the water out of compounds
containing hydrogen and oxygen. We saw this in class when we added sulfuric acid
to sucrose (sugar). The acid sucked out the water leaving charcoal behind.
If we do the same thing to ethanol, sulfuric acid will suck out as much water
as it can, but there will be leftover hydrogens. Two reactions are possible, depending on temperature:

H2SO4

2 CH3CH2OH

----->

CH3CH2OCH2CH3

+

H2O

H2SO4

CH3CH2OH

----->

H2C=CH2

+

H2O

The sulfuric acid is written over the arrow to show that it promotes the reaction
but is not changed by the reaction. In this case, it serves simply to remove
the water produced by the reaction.

The product H2C=CH2, ethylene, is a gas and it is a feedstock
for a great deal of industrial chemistry. U.S. production of ethyene was 15.9 billion kg
in 1989, the fourth largest volume.
It is used mainly to produce polyethylene, the plastic from which milk cartons
are made. While it could be produced from ethanol as described, it is more economical
to produce it from petroleum. With no polar OH groups, it is, of course, not
soluble in water.

Charge Distribution

Ball and Stick

Structural Formula

H H
| |
C=C
| |
H H

Formula

CH2CH2

Emprirical Formula

CH2

The product CH3CH2OCH2CH3 is ethyl ether,
or just ether for short. It is a very popular laboratory solvent. Because
of its combination of flammability and low boiling point, it poses an explosion
hazard. Cocaine users use this solvent when "free basing" and there have been
several celebrity explosions from careless use of ether. It is also used as
an anesthetic in its own right. Since it has no OH group, it is non-polar
and insoluble in water.

Charge Distribution

Ball and Stick

Structural Formula

H H H H
| | | |
H-C-C-O-C-C-H
| | | |
H H H H

Formula

CH3CH2OCH2CH3

Emprirical Formula

C4H10O

Esters

Just as an acid and an alkali react to form a salt, an organic acid and an alcohol
react to form an ester. Fats, for example, were esters of glycerol
and three fatty acids. When acetic acid and ethanol react, they form ethyl acetate.
Notice that this naming convention follows the same "first name-last name"
form that we used for inorganic salts.

Instructions

You will distill 500 mL of your own mead. There is a still set up in Gilmer 213
which you may use only during the designated period.
You may not remove
any alcohol from the lab!
Dr. Dunn must personally monitor all distillations.

Procedure:

Alert Dr. Dunn that you are ready to distill.

Measure out 500 mL of mead and pour it into the pot. Make sure there are
boiling chips in the pot.

Assemble the rest of the still and turn on the cooling water.

Turn on the Variac and set it to 70%.

When the mead begins to boil, turn the variac down to 50%.

Monitor the temperature. When it reaches 78 C, the first drops of ethanol
will distill over. The temperature may gradually rises during the course of the
distillation. Wait until alcohol stops dripping into the receiver and then turn off
the Variac.

Allow Dr. Dunn to test the alcohol content of your product.

When the pot has cooled, pour any "spent" mead down the drain.
Rinse the pot and make sure to return the boiling chips.

Pour your alcohol product into the designated container. Again: do not
remove alcohol from the lab!

Criteria for Success

Mead will not burn, but ethanol will. I will attempt to light your "beeshine."
If it burns, you pass. If not, you fail.
But of course you can try again (once per day).